1. Steering System Ackerman Linkage geometry Road wheel geometry Caster
Kingpin inclination
Compliance effects

2. Ackerman Steer d = tan-1 ----- = ----- o d d o iL L
d = tan = ----- o d
R+t/2 o d i
R+t/2 L L
d = tan = ----- i
R-t/2
R-t/2
For large radii, R >> t/2 L
d = --
Ack R L R
Turn
Center
t/2

3. Ackerman – Truck Steering System
Straight ahead
Right turn
Left turn

4. Ackerman Steer
50%
Parallel
Ackerman

5. Car Steering Systems Rack and pinion Gearbox Steering arm Rack
Tire rod
Tire rod
Gearbox
Steering arm
Pitman arm
Idler arm
Relay link

6. Truck Steering Systems
Tire rod
Steering arm
Gearbox
Pitman arm
Drag link

7. Compliance in Steering System

8. Geometry at the Wheel

9. Lateral Inclination Angle

10. Torques from Lateral Inclination

11. Caster Angle

12. Torques from Caster Angle

13. Lateral Force

14. Tractive Force

15. 4 Wheel Steer - Low Speed
R = L
d (1 + d /d ) f r

16. 4 Wheel Steer - High Speed
Four-wheel in-phase steering
Only at high speed (typically above 35 mph)
Rear steer angles less than front
Rear steer angles limited to a few degrees

17. Steering System Applications
Effect of steering geometry on performance
Understeer (linear range)
Limit cornering (non-linear range)
Steering torques and feel
On-center feel
Torque gradients
Linearity
Power assist characteristics
Friction and damping
Evaluate effects of asymmetry
Manufacturing tolerance

18. Steering Ratio
Steering Ratio = Steering wheel angle (deg) / Road wheel angle (deg)
Steering ratio for cars = 15 to 20
Steering ratio for trucks = 20 to 40

19. Steering Ratio

20. Assignment
Design linkage geometry to meet requirement of the minimum turn radius and provide close to Ackerman geometry (X-Y plane is ok)
Design steering ratio with measurements on your car